Structural morphology and compaction of nascent high-density polyethylene produced by supported catalysts

The morphologies of three nascent high-density polyethylene (HDPE) powders, polymerized in the gas phase by different catalysts, were investigated using scanning electron microscopy (SEM). Silica-supported catalyst systems comprising TiCl₄/MgCl₂,bis(triphenylsilyl)chromate andbis(cyclopentadienyl)chromium were found to produce polymers with globular, nodular and worm-like microstructures, respectively. The topographies of the fluff particles are related to the compaction behaviour of the HDPE powders. Long, worm-like strands that protrude from the particles are capable of forming more extensive entanglements than the shorter, nodular structures. The entanglements are the main cause of agglomeration of the particles during their long-term bulk storage. Furthermore, the rate of thermal oxidation is influenced markedly by the polymer microstructure. The microstructure determines the surface area available for oxygen attack. High-resolution SEM combined with low-temperature plasma etching reveals that the worm-like structures consist of folded-chain lamellae that are coiled around a core of extended chains.     

Influence of the Association of Rigid and Flexible Macromolecules on Their Compatibility

Consideration is given to a melt of rigid rodlike macromolecules whose side mainchain links are capable of associating with active end groups of flexible chains (it is assumed that each flexible chain has only one active end group), thus forming associated complexes. It is shown that with decrease in the temperature the association facilitates substantial improvement in the compatibility of rigid and flexible molecules in the melt.     

Statistics of Polymer‐Chain Conformations in the Intrinsic Coordinate System

The statistics of polymerchain conformations in the intrinsic coordinate system, the directions of whose axes are determined by the anisotropy of a polymer coil at certain instantaneous distribution of the conformations, is considered. It is shown that even for an absolutely flexible polymer chain the shape of the coil in the intrinsic coordinate system is anisotropic. Full distribution functions of the chain links in space are constructed for both the absolutely flexible linear polymer and the linear polymer chain which possesses finite flexural rigidity, and degrees of anisotropy of these macromolecules are calculated.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

Highly Thermoconductive,Thermostable, and Super-Flexible Film by Engineering 1D Rigid Rod-Like Aramid Nanofiber/2D Boron Nitride Nanosheets

Polymer-based thermal management materials have many irreplaceable advantages not found in metals or ceramics, such as easy processing, low density, and excellent flexibility. However, their limited thermal conductivity and unsatisfactory resistance to elevated temperatures (<200 °C) still prevent effective heat dissipation during applications with high-temperature conditions or powerful operation. Therefore, herein highly thermoconductive and thermostable polymer nanocomposite films prepared by engineering 1D aramid nanofiber (ANF) with worm-like microscopic morphologies into rigid rod-like structures with 2D boron nitride nanosheets (BNNS) are reported. With no coils or entanglements, the rigid polymer chain enables a well-packed crystalline structure resulting in a 20-fold (or greater) increase in axial thermal conductivity. Additionally, strong interfacial interactions between the weaved ANF rod and the stacked BNNS facilitate efficient heat flux through the 1D/2D configuration. Hence, unprecedented in-plane thermal conductivities as high as 46.7 W m⁻¹ K⁻¹ can be achieved at only 30 wt% BNNS loading, a value of 137% greater than that of a worm-like ANF/BNNS counterpart. Moreover, the thermally stable nanocomposite films with light weight (28.9 W m⁻¹ K⁻¹/10³ (kg m⁻³)) and high strength (>100 MPa, 450 °C) enable effective thermal management for microelectrodes operating at temperatures beyond 200 °C.     

含1,3,5-三嗪结构聚芳醚高性能聚合物的合成

1,3,5-三嗪基聚合物具有优异综合性能,但传统1,3,5-三嗪基聚合物难溶解、难熔融,通常在高温高压下才能制得高分子量聚合物,限制了其在分离膜、绝缘漆和粘合剂等领域的应用。文中基于分子设计理论,分别在聚合物分子链中引入柔性侧基、非对称性结构、扭曲或扭曲非共平面结构等,合成了系列既耐高温又可溶解的含1,3,5-三嗪结构新型聚芳醚高性能聚合物,探讨了分子结构等对聚合物溶解性、热性能和力学性能间影响规律。     

On the crystal texture of linear polyaryls (PEEK,PEK and PPS)

Three linear ppolyaryls, polyetheretherketone (PEEK) polyetherketone (PEK) and polyphenylenesulphide (PPS) have been examined regarding crystal morphologies as obtained from solutions and molecular orientation in melt grown spherulites, the latter involving also experiments on the carbon fibre containing polymer. In addition to the individual features observed in solution grown crystals agreeing with those being reported concurrently from elsewhere, the present coordinated results on three polymers underline the common crystallization behaviour and texture for this family of polymers. These common features comprise the existence of lamellae as symptomatic of chain folding, acicular shapes indicative of uniaxial growth (b being the growth direction in all three cases), and irregular crystal edges. The sheaf development of these crystals then leads readily to a postulated radiolb-axis orientation in spherulites, confirmed directly in melt crystallized samples possessing transcrystalline textures induced by nucleating carbon fibres. Observations on the effect of carbon fibres drew our attention to the combined influence of the crystal nucleating effect and separation distance of these fibres on the resulting crystal texture of the polymer matrix: varying the relative magnitude of the two effects, can even reverse the overall crystal orientation in the sample. Such considerations should be pertinent to crystal texture development in composites with crystaallizable thermoplastic matrices in general.     

Molecular Design of Antifouling Polymer Brushes Using Sequence‐Specific Peptoids

Material systems that can be used to flexibly and precisely define the chemical nature and molecular arrangement of a surface would be invaluable for the control of complex biointerfacial interactions. For example, progress in antifouling polymer biointerfaces that prevents nonspecific protein adsorption and cell attachment, which can significantly improve the performance of an array of biomedical and industrial applications, is hampered by a lack of chemical models to identify the molecular features conferring their properties. Poly(N‐substituted glycine) “peptoids” are peptidomimetic polymers that can be conveniently synthesized with specific monomer sequences and chain lengths, and are presented as a versatile platform for investigating the molecular design of antifouling polymer brushes. Zwitterionic antifouling polymer brushes have captured significant recent attention, and a targeted library of zwitterionic peptoid brushes with different charge densities, hydration, separations between charged groups, chain lengths, and grafted chain densities, is quantitatively evaluated for their antifouling properties through a range of protein adsorption and cell attachment assays. Specific zwitterionic brush designs are found to give rise to distinct but subtle differences in properties. The results also point to the dominant roles of the grafted chain density and chain length in determining the performance of antifouling polymer brushes.     

Stretched polymer nanohairs by nanodrawing

A simple, yet innovative, method is presented for fabricating high-aspect-ratio polymer nanohairs (aspect ratio >20) on a solid substrate by sequential application of molding and drawing of a thin polymer film. The polymer film was prepared by spin coating on a rigid or flexible substrate, and the temperature was raised above the polymer's glass transition while in conformal contact with a poly(urethane acrylate) mold having nanocavities. Consequently, capillary forces induced deformation of the polymer melt into the void spaces of the mold and the filled nanostructure was further elongated upon removal of the mold due to tailored adhesive force at the mold/polymer interface. The optimum value of the work of adhesion at the mold/polymer interface ranged from 0.9 to 1.1 times that at the substrate/polymer interface.     

Model systems for single molecule polymer dynamics

Double stranded DNA (dsDNA) has long served as a model system for single molecule polymer dynamics. However, dsDNA is a semiflexible polymer, and the structural rigidity of the DNA double helix gives rise to local molecular properties and chain dynamics that differ from flexible chains, including synthetic organic polymers. Recently, we developed single stranded DNA (ssDNA) as a new model system for single molecule studies of flexible polymer chains. In this work, we discuss model polymer systems in the context of "ideal" and "real" chain behavior considering thermal blobs, tension blobs, hydrodynamic drag and force-extension relations. In addition, we present monomer aspect ratio as a key parameter describing chain conformation and dynamics, and we derive dynamical scaling relations in terms of this molecular-level parameter. We show that asymmetric Kuhn segments can suppress monomer-monomer interactions, thereby altering global chain dynamics. Finally, we discuss ssDNA in the context of a new model system for single molecule polymer dynamics. Overall, we anticipate that future single polymer studies of flexible chains will reveal new insight into the dynamic behavior of "real" polymers, which will highlight the importance of molecular individualism and the prevalence of non-linear phenomena.     

Polyethylene-polyethylene microfibrillar composites

Solid-state drawing of melt-crystallized, or gel(solution)-crystallized, polyethylene (PE) is well established as a means of producing high modulus high-strength fibres. Here, an alternative route, based on melt-processing, is reviewed and its merits are assessed. Contrary to expectation, melt processing of flexible chain polymers can directly yield oriented products with good mechanical properties, without the need for post-drawing in the solid state. The melt-processed PE can give a special microfibrillar composite morphology which results in good mechanical properties. The paper also reviews aspects of composites design by comparing these microfibrillar composites with traditional fibre composites and molecular composites.Dedicated to professor Andrew Keller, FRS, after retirement, as a mark of appreciation for his contributions to the understanding of polymer crystallization, and for allowing us to learn about the subject and encouraging our investigations in a general research environment at Bristol.     

Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High‐Efficiency Polymer Solar Cells

Suppression of carrier recombination is critically important in realizing high‐efficiency polymer solar cells. Herein, it is demonstrated difluoro‐substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D‐conjugated D–A copolymer J91 is designed and synthesized with bi(alkyl‐difluorothienyl)‐benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low‐lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n‐type organic semiconductor acceptor m ‐ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high V _OC of 0.984 V and high J _SC of 18.03 mA cm^?2 is obtained for the polymer solar cells based on J91 /m ‐ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.     

Polymer-layered silicate nanocomposites in the design of antimicrobial materials

A robust processing of polymers into antimicrobial materials is introduced using polymer/clay nanotechnology. Antimicrobial activity of commercially available organoclays modified with cationic surfactants has been screened in tests against gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria. Despite the leaching biocidal surfactants, cell interactions with organoclay surface have been identified to be responsible for antimicrobial activity of organoclays. Distribution of clay platelets within polymer matrix by melt extrusion process resulted in polymer/clay nanocomposites active against both gram-positive and gram-negative bacteria by contact. The study discloses a much overlooked function of organoclays modified with cationic surfactants for nanocomposite application, i.e., the ability of organoclays to render polymer nanocomposites biocidal.     

Electron Transfer Mediated by Surface‐Tethered Redox Groups in Nanofluidic Devices

Electrochemistry provides a powerful sensor transduction and amplification mechanism that is highly suited for use in integrated, massively parallelized assays. Here, the cyclic voltammetric detection of flexible, linear poly(ethylene glycol) polymers is demonstrated, which have been functionalized with redox‐active ferrocene (Fc) moieties and surface‐tethered inside a nanofluidic device consisting of two microscale electrodes separated by a gap of <100 nm. Diffusion of the surface‐bound polymer chains in the aqueous electrolyte allows the redox groups to repeatedly shuttle electrons from one electrode to the other, resulting in a greatly amplified steady‐state electrical current. Variation of the polymer length provides control over the current, as the activity per Fc moiety appears to depend on the extent to which the polymer layers of the opposing electrodes can interpenetrate each other and thus exchange electrons. These results outline the design rules for sensing devices that are based on changing the polymer length, flexibility, and/or diffusivity by binding an analyte to the polymer chain. Such a nanofluidic enabled configuration provides an amplified and highly sensitive alternative to other electrochemical detection mechanisms.     

Modelling mechanical characteristics of microbial biofilms by network theory

In this contribution, we present a constitutive model to describe the mechanical behaviour of microbial biofilms based on classical approaches in the continuum theory of polymer networks. Although the model is particularly developed for the well-studied biofilms formed by mucoid Pseudomonas aeruginosa strains, it could easily be adapted to other biofilms. The basic assumption behind the model is that the network of extracellular polymeric substances can be described as a superposition of worm-like chain networks, each connected by transient junctions of a certain lifetime. Several models that were applied to biofilms previously are included in the presented approach as special cases, and for small shear strains, the governing equations are those of four parallel Maxwell elements. Rheological data given in the literature are very adequately captured by the proposed model, and the simulated response for a series of compression tests at large strains is in good qualitative agreement with reported experimental behaviour.     

Development of minimal models of the elastic properties of flexible and stiff polymer networks with permanent and thermoreversible cross-links

We review the elasticity of flexible and stiff polymer networks with permanent cross-links and synthesize these results into a unifying polymer chain network model. This framework is then used to address how the network elasticity becomes modified when the network cross-linking is thermoreversible in nature, changes in the stability of the network with deformation, and the effect of a variable rate of network deformation on the non-linear elastic response. Comparisons are made between this class of simplified network models with elasticity measurements performed on flexible chain and stiff fiber networks, both with permanent and associative cross-links. Although these network models are highly idealized, they are apparently able to capture many aspects of the elastic properties of diverse real networks.     

Modifizierung des ABSE‐Polycarbosilazans mit Multi‐Walled Carbon Nanotubes zur Herstellung spinnfähiger Massen

Modification of the ABSE polycarbosilazane with multi‐walled carbon nanotubes for the creation of spinable masses An inexpensive method has been found to produce ceramic SiCN‐fibres via the precursor route consisting of five processing steps: synthesis of the polymer, preparation of the spinning mass, melt‐spinning, curing via electron beam and subsequent pyrolysis at 1100 °C in a nitrogen atmosphere. A special solid and meltable fibre polymer, the so‐called polycarbosilazane ABSE, has been developed in the last decade for this purpose. Due to its low molecular weight, an adequate catalytic and thermal aftertreatment was necessary to guarantee a stable melt‐spinning process. This article discusses an alternative way to prepare a qualified spinning mass, i.e. the addition of Multi‐Walled Carbon Nanotubes (MWCNTs) to the ABSE melt. For this purpose a homogeneous dispergation of the MWCNTs in the ABSE matrix is necessary. In this study, spinning masses were fabricated in different ways. By optical analysis and comparison of the level of dispergation in these spinning masses an optimized process for integration of the MWCNTs was identified. The influence of the addition of a dispersing agent is investigated as well. In using a dispersing agent, the level of homogeneous dispersion of the MWCNTs increases whereas the interactions between the particles and the precursor melt decrease. In first spinning experiments a good spinability of the masses were noticed. Thus the addition of MWCNTs represents a new way to modify the ABSE precursor for the melt‐spinning process.     

Modification of nylon-6 with semi-rigid and wholly-rigid aromatic polyamides

Nylon-6 was reinforced by two semi-rigid aromatic polyamides, poly(p-diphenylmethyl terephthalamide) (PMA), and poly(p-diphenyloxide terephthalamide) (POA), and also one wholly-rigid aromatic polyamide, poly(m-phenylene isophthalamide) (PmlA) by physical blending and chemical copolymerization usingp-amino phenyl acetic acid (P-APA) as a coupling agent. From the results of differential scanning-calorimetry, it was shown that both the polyblends with semi-rigid and wholly-rigid polyamides exhibited a glass transition temperature,Tg, higher than that of nylon-6 homopolymer. It also showed that theT _gs of wholly-rigid polyblends were higher than those of semi-rigid polyblends. Nevertheless, the multiblock copolyamides appeared to have even higherT _g andT _m, and better thermal stability. Morphological observations revealed that all the polymer alloys (polyblends and copolymers) were a dispersed phase structure, although the multiblock copolyamides were more homogeneous and compatible. Based on wide-angle X-ray diffraction, it was found that the polyblends had two diffraction peaks, i.e. 2 = 20.5 ° and 24 °. However, the multiblock copolyamides had only one peak at 2 = 20 °, evidently indicating a new crystal structure of the multiblock copolyamides formed. For the mechanical properties, it was found that the multiblock copolyamides had a more significant reinforcing effect than those of polyblends, especially those copolymerizing with wholly aromatic polyamides.     

Aliphatic Polycarbonate‐Based Solid‐State Polymer Electrolytes for Advanced Lithium Batteries: Advances and Perspective

Conventional liquid electrolytes based lithium‐ion batteries (LIBs) might suffer from serious safety hazards. Solid‐state polymer electrolytes (SPEs) are very promising candidate with high security for advanced LIBs. However, the quintessential frailties of pristine polyethylene oxide/lithium salts SPEs are poor ionic conductivity (≈10⁻⁸ S cm⁻¹) at 25 °C and narrow electrochemical window (<4 V). Many innovative researches are carried out to enhance their lithium‐ion conductivity (10⁻⁴ S cm⁻¹ at 25 °C), which is still far from meeting the needs of high‐performance power LIBs at ambient temperature. Therefore, it is a pressing urgency of exploring novel polymer host materials for advanced SPEs aimed to develop high‐performance solid lithium batteries. Aliphatic polycarbonate, an emerging and promising solid polymer electrolyte, has attracted much attention of academia and industry. The amorphous structure, flexible chain segments, and high dielectric constant endow this class of polymer electrolyte excellent comprehensive performance especially in ionic conductivity, electrochemical stability, and thermally dimensional stability. To date, many types of aliphatic polycarbonate solid polymer electrolyte are discovered. Herein, the latest developments on aliphatic polycarbonate SPEs for solid‐state lithium batteries are summarized. Finally, main challenges and perspective of aliphatic polycarbonate solid polymer electrolytes are illustrated at the end of this review.     

Semi-rigid––simply supported shear deformable pultruded GRP beams subjected to end moment loading: comparison of measured and predicted deflections

A single span shear deformable beam is analysed. One end is simply supported and subjected to an external moment and the other is supported by a semi-rigid joint with a linear moment––rotation characteristic. An expression for the mid-span deflection is derived in order to predict deflections recorded in tests on pultruded GRP beams with four types of semi-rigid joint. Using rotational stiffnesses derived from moment––rotation tests on similar joints it is shown that semi-rigid, shear deformable beam analysis is generally able to predict the measured deflections to within less than 10%. The mid-span deflection formula is recast to allow a back analysis to be carried out to determine the actual stiffness of two of the semi-rigid joints. It is shown that the joint tests significantly under-estimate the rotational stiffness of the bolted web cleat joint, whereas the predicted stiffness of the bolted web and flange cleat connection differs only by about 20% from that determined in one of the joint tests on this connection.